stds-802-16: sub10. Proposal for the Duplexing Scheme

[vicente.quilez_sanchez@alcatel.es]

     When comparing TDD and FDD duplexing alternatives, following 
     considerations are relevant:
     
     1.  TDD allows asymmetrical traffic: When dealing with asymmetrical 
     traffic flow, as it is today for Internet-based data traffic, in which 
     the volume of information sent in the downlink direction is much 
     higher as compared to the corresponding volume sent in the uplink 
     direction, TDD allows to fully exploit the usage of the resources 
     (i.e. radiochannels), while in the FDD case this asymmetry can not be 
     matched in an efficient manner, given the inherent symmetrical nature 
     of FDD. This asymmetrical characteristic depends on the type of 
     application, but it is very significative, specially for SoHo and 
     Residential markets, because these market segments are the ones which 
     are reflected best in the client-server model
     
     2.  TDD provides more flexibility for spectrum usage: Frequency 
     spectrum is an increasingly scarce resource. More and more often, it 
     is difficult to obtain paired bands available for new applications. 
     TDD can make use of both paired and unpaired slots in the spectrum, 
     while FDD necessarily has to match paired bands. In particular TDD is 
     the chosen duplexing approach for the US MMDS band, possibly the most 
     important frequency band for IEEE 802.16sub10. 
     
     3.  TDD provides better economies: A switch is cheaper than a 
     duplexer, and this has had a direct impact for the cost of the CPE 
     equipment, the key element when computing the global cost per user. 
     Therefore TDD-based systems will inherently provide cheaper solutions 
     than FDD-based systems. Economy is always very important, but it is 
     particularly key for SoHo and Residential markets, given the continuos 
     trend of tremendous reduction costs of competing technologies such as 
     ADSL.
     
     4.  TDD allows to concentrate most of the air interface 
     related-process in the infrastructure, as channel behaviour can be 
     extrapolated from uplink into downlink and viceversa. This functional 
     partitioning open the possibility for further improving the economies 
     for CPE equipment
     
     
     Based on the reasons above, it is proposed than IEE 802.6sub10 adopts 
     a TDD duplexing scheme
     
     
     Vicente Quilez
     Alcatel
     veq@alcatel.es